Composite self-healing system

ABSTRACT

An advanced reflexive structure system is disclosed. The reflexive system mimics the pain withdrawal reflex on which the human body relies. The reflexive system incorporates a continuous health and performance monitoring system via an embedded dielectric film, an adaptive composite structure based on shape memory composite material, and an intelligence system which will be interfaced with both the health/performance sensors and the adaptive structure. When activated shape memory polymer will recover its structural integrity via shape recovery and a reptation healing process. These features enable the use of SMP as an adaptive structure in the proposed reflexive system. The development of a reflexive system for structures will enable increased safety and security and demonstrate a better understanding of integrated performance systems. This reflexive technology could find immediate implementation on all current and future systems and future implementation on platforms such as the International Space Station, Lunar, and Martian habitats.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority from U.S. Provisional Application Ser.No. 60/911,673 filed Apr. 13, 2007, U.S. Provisional Application Ser.No. 60/911,682 filed Apr. 13, 2007, and U.S. Provisional ApplicationSer. No. 60/911,665 filed Apr. 13, 2007.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

This invention was made with U.S. Government support under Contract No.NNL05AA97C awarded by National Aeronautics and Space Administration andContract No. NNL06AA07C awarded by the National Aeronautics and SpaceAdministration to Cornerstone Research Group Inc. The U.S. Governmenthas certain rights in the invention.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This application relates to the self-repair of polymer and polymercomposite structures. The disclosed method of achieving this is todesign and incorporate smart, intelligent, and adaptive systems into thestructures composed of adaptive materials such as dynamic modulus resinsand composites. Such systems will allow for continuous health andperformance monitoring, fast and decisive information processing toensure that the system is “highly aware” of its current health statusand unparalleled in its adaptability to damage. Currently, moststate-of-the-art health monitoring technologies can only deliver theindication of damage to the human operator via visual display. Anintegrated system consisting of smart, adaptive, and intelligentcomponents will enable an advanced system to sense and immediatelyrecover from physical damage while informing the operator of thesituation but not requiring a response.

2. Description of Related Art

Dynamic Elastic Modulus Resins (DMR) are resins whose elastic moduluschanges with a change in temperature of the resin. One such DMR is shapememory polymer (SMP). Shape memory materials were first developed abouttwenty-five (25) years ago and have been the subject of commercialdevelopment in the last fifteen (15) years. Shape memory materialsderive their name from their inherent ability to return to theiroriginal “memorized” shape after undergoing a shape deformation. Thereare principally two types of shape memory materials, shape memory alloys(SMAs) and shape memory polymers (SMPs).

SMAs and SMPs that have been pre-formed can be more easily deformed to adesired shape above their glass transition temperature (Tg). The SMA andSMP must remain below, or be quenched to below, the Tg while maintainedin the desired shape to “lock” in the deformation. Once the deformationis locked in, the SMA, because of its crystalline network, and the SMP,because of its polymer network, cannot return to a relaxed state due tothermal barriers. The SMA and SMP will hold its deformed shapeindefinitely until it is heated above its Tg, whereupon the SMA and SMPstored mechanical strain is released and the SMA and SMP returns to itspre-formed, or memory, state.

There are principally two types of plastics, thermoset resins andthermoplastic resins, each with its own set of unique characteristics.Thermoset resins, for example polyesters, are liquids that react with acatalyst to form a solid, and cannot be returned to their liquid state,and therefore, cannot be reshaped without destroying the polymernetworks. Thermoplastics resins, for example PVC, are also liquids thatbecome solids. But unlike thermoset resins, thermoplastics are softenedby application of heat or other catalysts. Thermoplastics can be heated,reshaped, heated, and reshaped over and over.

SMPs used in the presently disclosed method and devices are uniquethermosetting polymers that, unlike traditional thermosetting polymers,can be reshaped and formed to a great extent because of their shapememory nature and will not return to a liquid upon application of heat.Thus by creating a shape memory polymer that is also a thermosettingpolymer, designers can utilize the beneficial properties of boththermosetting and thermoplastic resins while eliminating or reducing theunwanted properties. Such polymers are described in U.S. Pat. No.6,759,481 issued to Tong, on Jul. 6, 2004 which is incorporated hereinby reference. Other thermoset resins are seen in PCT Application No.PCT/US2006/062179, filed by Tong, et al on Dec. 15, 2006; and PCTApplication No. PCT/US2005/015685 filed by Tong et al, on May 5, 2005 ofwhich both applications are incorporated herein by reference.

Additionally DMRs and SMPs can self-heal through combination of shapememory effects and a reptation process. Reptation theory describes thesnake-like large-scale motion of long-chain entangled polymers across aninterface, involving interfacial bonding across a boundary. Thediffusive motion of polymer segments across a boundary is increased athigh temperatures in which long-chain polymers are embedded. Essentiallythis motion allows two polymer surfaces to bond together along theirinterface when placed in intimate contact above the Tg of the polymer.This phenomenon commonly referred to as “healing” is essentially theinterfacial welding of two polymer surfaces through the inter-diffusionof the polymer by motions across the interface via chain reptation-typemotions. This basic picture of reptation is by now experimentallyverified and well-established in many contexts.

This form of healing is commonly studied when polymers are placed incontact above Tg. As samples are heated and expand, the crack surfacescome into intimate contact and healing progresses following thediffusion process described above, mending the crack. The Tong patentsmentioned above can be formulated by those of skill in the art toinclude this self-healing feature.

There are three types of SMP's: 1) A partially cured resin, 2)thermoplastics, and 3) fully cured thermoset systems. There arelimitations and drawbacks to the first two types of SMP. Partially curedresins continue to cure during operation and change properties withevery cycle. Thermoplastic SMP “creeps,” which mean it gradually“forgets” its memory shape over time. A thorough understanding of thechemical mechanisms involved will allow those of skill in the art totailor the formulations of SMP to meet specific needs, althoughgenerally fully cured thermoset resin systems are preferred inmanufacturing.

While SMA and SMP appear to operate similarly on the macro scale, at themolecular scale it is apparent that the method of operation of each isvery different. The difference between SMA and SMP at the molecularlevel is in the linkages between molecules. SMA essentially has fixedlength linkages that exist at alternating angles establishing in azigzag patterned molecular structure. Reshaping is achieved bystraightening the angled connections from alternating angles to straightforming a cubic like structure. This method of reshaping SMA materialenables bending while limiting any local strains within the SMAmaterials to less than eight percent (8%) strain, as the maximum shapememory strain for SMA is eight percent (8%). This eight percent (8%)strain allows for the expansion or contraction of the SMA by only 8%, astrain that is not useful for most industrial applications. Recovery tomemory shape is achieved by heating the material above a certaintemperature at which point the molecules return to their original zigzagmolecular configuration with significant force thereby reestablishingthe memory shape. The molecular change in SMA is considered a metallicphase change from Austensite to Martensite which is defined by the twodifferent molecular structures.

SMP has connections between molecules with some slack. When heated theselinks between connections are easily contorted, stretched and reorienteddue to their elastic nature as the SMP behaves like an elastic materialwhen heated, when cooled, the shape is fixed to how it was being held.In the cooled state the material behaves as a typical rigid polymer thatwas manufactured in that shape. Once heated the material again returnsto the elastic state and can be reformed or return to the memory shapewith very low force. Unlike SMA which possesses two different molecularstructures, SMP is either a soft elastomer when heated or a rigidpolymer when cool. Both SMA and SMP can be formulated to adjust theactivation temperature for various applications. Critical to the successof the currently claimed device is thermoset SMP which provides an orderof magnitude higher stiffness than previous state-of-the-artthermoplastic SMPs. This added stiffness coupled with high straincapability enables the development and use of a highly useful compositetooling technology.

Unlike SMAs, SMPs exhibit a radical change from a normal rigid polymerto a flexible elastic and back on command. SMA would be more difficultto use for most applications because SMAs do not have the ease inchanging the activation temperature as do SMP's. SMAs would also haveissues with galvanic reactions with other metals which would lead tolong term instability. The current supply chain for SMAs is currentlynot consistent as well. SMP materials offer the stability andavailability of a plastic and are more inert than SMAs. Additionally,when made into a composite SMPs offer similar if not identicalmechanical properties to that of traditional metals and SMAs inparticular. Throughout this disclosure SMP and SMP composites are usedinterchangeably as each can be replaced by the other depending on thespecific design requirements to be met.

The term “composite” is commonly used in industry to identify componentsproduced by impregnating a fibrous material with a thermoplastic orthermosetting resin to form laminates or layers. Generally, polymers andpolymer composites have the advantages of weight saving, high specificmechanical properties, and good corrosion resistance, which make themindispensable materials in all areas of manufacturing. Nevertheless,manufacturing costs are sometimes detrimental, since they can representa considerable part of the total costs and are made even more costly bythe inability to quickly and easily repair these materials withoutrequiring a complete, and expensive, total replacement. Because SMPs areresins, they can be used to make composites, which are referred to inthis application as SMP composites.

Advanced composites, containing continuous fibers dispersed in a resinmatrix material, are widely used in aerospace, sports equipment,infrastructure, automotive, and other industries both as primary andsecondary load-bearing structures. These composite materials derivetheir excellent mechanical strength, stiffness, and other propertiesfrom a combination of the resin and reinforcement fibers used. Theaddition of reinforcements such as continuous fiber, fiber mats, choppedfibers, fiberglass, nanoparticles and other similar material is known.Even with nanoparticles like carbon nanotubes and carbon nano-fillers asmall amount of these nano-fillers could dramatically alter theproperties of a matrix resin.

A recurring issue in product applications using materials such aspolymeric materials is that they tend to fail or degrade due tomechanical fatigue, mechanical impact, oxidation due to radiation orimpurities, thermal fatigue, chemical degradation, or a combination ofthese processes. The degradation can lead to embrittlement of thepolymer along with other adverse effects. The embrittlement andassociated cracking can advance to a point that it causes productfailure and associated replacement costs. Thermoplastic and thermosetpolymer systems used in products can be particularly susceptible tothese failures.

This problem is of great concern because of the widespread and intensiveuse in modern society of polymers and polymer composites in productcomponents. Traditional approaches to increasing the reliability ofpolymeric based components and products have included a focus onsuitable design enhancements and the use of incrementally improvedplastics.

One recently developed process to impart self-healing capability to apolymer involves the incorporation of microcapsules containing a healingagent in a polymer matrix. When a fracture occurs in the polymer matrixin close proximity to the microcapsules the associated stresses causedby the fracture ruptures the microcapsules. As a consequence the healingagent is released from the ruptured microcapsules and contacts thefracture surfaces. At the same time the healing agent comes into contactwith a polymerization agent dispersed in the polymer matrix. Thepolymerization agent is functionally active in the presence of variouschemicals including moisture in the air. When the polymerization agentcontacts the self-healing agent and promotes polymerization of thehealing agent resulting in filling the crack planes of the fracture.

U.S. Pat. No. 7,285,306 issued on Oct. 23, 2007 to Parrish discloses aself-healing system for an insulation material wherein the self repairprocess is initiated by rupturing a plurality of microcapsules disposedon the insulation material. When a plurality of microcapsules isruptured, reactants within the plurality of microcapsules react to forma replacement polymer in a break of the insulation material.

U.S. Pat. No. 7,108,914 issued on Sep. 19, 2006 to Skipor et al. alsodiscloses a self-healing polymer composition containing a polymer mediaand a plurality of microcapsules of flowable polymerizable materialdispersed in the polymer media, where the microcapsules of flowablepolymerizable material containing a flowable polymerizable material andhave an outer surface upon which at least one polymerization agent ischemically attached. The microcapsules are effective for rupturing witha failure of the polymeric media and the flowable polymerizable materialreacts with the polymerization agent when the polymerizable materialmakes contact with the polymerization agent upon rupture of themicrocapsules.

The principal drawback of Parrish and Skipor is that once themicrocapsules have ruptured and repaired the insulation a second breakor damage point at or near the first break or damage point cannot be aseasily repaired because the replacement polymers in the microcapsuleswill have been used in the first repair.

U.S. Pat. Nos. 6,261,360; 5,989,334; 5,660,624; 5,575,841; and 5,5611,73issued to Dry describe a cured composite matrix having a plurality ofhollow release vessels usually fibers dispersed therein with the hollowfibers having a selectively releasable modifying agent contained withinthem a means for maintaining and modifying agent within the fibers untilselectively released and a means for permitting selective release of themodifying agent from the hollow fibers into the matrix material inresponse to at least one predetermined external stimulus. The curedmatrix materials have within them fibers capable of delivering repairagents into the matrix wherever and whenever they are needed.

While this engineered healing composite represents a very excitingadvance in the self-repair of materials, it is limited to crack-typedamage and would not be expected to heal the large sized projectiledamage (several mm or more in diameter) or repair damage at the samepoint multiple times. The biggest difference between these patent andthe presently disclosed system is the fact that the presently disclosedsystem is known to heal via a thermo-mechanical response rather than bychemical reaction.

International Application No. PCT/US2005/0198 filed Jun. 6, 2005describes a manual process to repair damage in a material thought theapplication of a SMP or SMP composite patch. The pressure sensitiveadhesive placed on one side of the patch bonds the patch to the damagedarea, covering the damage. The SMP in the patch allows a human operatorto mold the patch to accurately fit the product being repaired. Thismethod is most useful for aesthetic repairs to a product, not forstructural repairs because the damage area will remain and couldpropagate beyond the boundaries of the patch at a future point.Additionally this device and method of repair requires a separate pieceof SMP or SMP composite and a human operator to effect repairs.

DISCLOSURE OF THE INVENTION

An advanced sense and respond technology comprised of multipletechnologies to enhance survivability of future systems constructed oflightweight resins or composites is disclosed. The system is designed toreact to detected damage with health monitoring by locally activatingshape recovery and healing mechanisms of the adaptive polymer matrix oradaptive polymer matrix composite structure through the use of provenhealth monitoring technology to sense the location and significance ofthe damage and new healable dynamic elastic polymers and dynamic elasticpolymers composites, an intelligent control system that integrates thesystem of technologies seamlessly and characterize the overalleffectiveness.

Reflexive response to the structural damage is introduced through thedesign of an electronic structural control system intended to mimic thereflex action of the human body. Through this system, a response tosensed structural damage will occur when a specific damage threshold isreached. Data interpretation and response will continue throughout themonitoring process by the structural control system, but only when thesensed damage reaches a limiting threshold will the reflexive repairsystem be activated.

A method for designing a product which can detect damage to the product,determine a course of action to heal the damage, selectively activatingthe components needed to heal the damage, allowing the material to heal,and detecting when healing is complete is disclosed.

Replacing traditional metallic structures with composites offers the enduser increased functionality including higher specific mechanicalproperties, customizable ply schedules for tailored properties, and lowcoefficient of thermal expansion. Introduction of composite materialsinto structural applications does however result in specific designconsiderations including failure mechanisms. The failure mechanism forcomposites, as compared to traditional structural materials includingconcrete and steel, are more difficult to predict and monitor for. Thischange in failure mechanism results in the necessity for expensive, andtime consuming, non destructive evaluation (NDE) to monitor structuralhealth. This requirement for NDE drives up the cost of compositeintegration therefore increasing the barrier to entry.

If a damage or fatigue failure is located in the structure the cost ofrepairing and or replacing the component can be extremely high as aresult of composites strength being derived from continuous fiber paths.The breaking of these fiber paths due to a repair can result in aweakening of the structure leading to reduced service life. Potentialproblems also arise with composite repairs made in place. If thestructure needs to remain in place during the repair, the potentialexists to require in place heating and pressure to cure the repair tothe composite. Also, during the repair of the composite time and moneyare lost as a result of the structure not being in service.

One method of achieving this is to design and incorporate smart,intelligent, and adaptive systems. Such systems will allow forcontinuous health and performance monitoring, fast and decisiveinformation processing to ensure that the system is “highly aware” ofits current health status and unparalleled in its adaptability to detectand repair damage. Currently, most state-of-the-art health monitoringtechnologies can only deliver the indication of damage to the humanoperator via visual display. An integrated system consisting of smart,adaptive, and intelligent components will enable an advanced missionsystem to sense and immediately recover from physical damage on-the-flywhile informing the operator of the situation but not requiring aresponse. Currently there is no method of recovering from physicaldamage due to an unforeseen event.

Conventional solutions to the problem of composite failure mechanismsand health monitoring have focused on integrating sensors to monitor thehealth of the composite structure. Examples of sensors that can beincorporated into a composite for monitoring purposes include; straingauges, piezoelectric fibers, and fiber optics. These techniques providean adequate level of structural understanding, however still require ahuman operator to interpret the results and make the appropriatedecision about structural capability. This process requires dedicatedpersonnel and results in time lags between when a structure is found tobe sub-par and when the structure can be repaired.

Upon determination from a human operator that a composite structure isno longer operating at 100% capacity it is required that either a newstructure be fabricated to replace the failed structure or a in placerepair is required. Repairs that are made while the structure is inplace requires that the structure be taken out of use while a compositeengineer can determine the appropriate fix for the structure and duringthe implementation of that repair. Currently, composite repairs can bedifficult as a result of elevated temperatures required to curecomposites as well as the necessity for a force to be applied during thecomposite cure for adequate fiber compaction. As a result of theserequirements, in place composite repair can be highly costly and timeconsuming.

A better approach to composite repair is modular structural design thatif a failure occurs in the structure, a modular section can be removedand replaced with a new section that can be fabricated at a separatelocation. This approach eliminates the necessity for costly in placecuring equipment as well as the potential elimination of having anengineer evaluate the structure since it will be replaced with the exactmaterial that was damaged. This process still does require the structureto be monitored by a human operator to determine if a failure hasoccurred as well as taking the necessary actions required to completethe structural repair. This approach also requires additional designtime to ensure that each aspect of the design is modular and has theability to be replaced section by section if required.

The reflexive system disclosed enables real time health monitoring of inuse composite structures as well as the ability to repair damage thusrestoring cold mechanical properties to the structure. The integrationof this system eliminates the need for a dedicated user, or team ofusers, to monitor the results of the integrated health monitoring systemas well as offers an in place repair capability. Having the repairmechanism in place greatly reduces the amount of time for repair throughthe elimination of needing to schedule a repair crew. Time is also savedthrough the way that a repair is conducted. Rather than having to eithercure a composite in place or remove a section and mechanically fasten anew section into place, repairs can be completed simply through theapplication of heat to the structure. It is for these reasons that bothtime and money are saved through this technology as well as aminimization of structural down time.

The idea for self repairing composites utilizing encapsulated fibers orbeads containing polymers and polymerization agent's are now widespread.However these systems are only as reliable and useful as long as thereis polymer remaining encapsulated within the composite or polymermatrix. Additionally once an area has repaired the damage with currentsystems there is little if any polymer remaining to repair a secondcrack or failure at the same point. Therefore there is a need for amethod and system for repairing a polymer or polymer compositerepeatably without the use of micro-encapsulated resins and polymers,without the application of additional resin or composite, and withoutthe interaction of a human operator.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the preferred heater panel design.

FIG. 2 shows the first layer of the preferred heater panel design.

FIG. 3 shows the second layer of the preferred heater panel design

FIG. 4 shows the third layer of the preferred heater panel design

FIG. 5 shows the fourth layer of the preferred heater panel design

FIG. 6 shows an electrical schematic of a three heater by three heatersection of the preferred heater panel design.

FIG. 7 is a perspective drawing showing damage to an aircraft wing.

FIG. 8 is perspective drawing showing the sensing system used to detectdamage in an aircraft wing.

FIG. 9 is a perspective drawing showing the heating system selectivelyactivating heaters to heal the damage in the aircraft wing.

FIG. 10 is a perspective drawing showing the sensing system detectingthat the damage has been healed.

FIG. 11 is a perspective drawing showing that the damage to the aircraftwing has been healed.

MODES FOR CARRYING OUT THE INVENTION

The presently disclosed method and devices utilizing the method are anadvanced reflexive structure technology system which increase thesurvivability of systems constructed of lightweight polymer and polymercomposite material. Applications of this device include a broadselection of high performance systems ranging from aircraft andspacecraft to habitats for space stations and interplanetary explorationin addition to commercial applications such as motor vehicles andbuilding components. The control system for the reflexive structuresmimics the pain withdrawal-reflex on which the human body relies. Thisis important because quick reaction is critical to survivability. Thissystem combines a damage sensing technology, a control system, a dynamicelastic modulus resin (DMR) matrix or a composite in a dynamic elasticmodulus resin matrix, and a means for activating the dynamic elasticmodulus resin matrix.

Dynamic Elastic Modulus Resins and Composites

One element of the claimed system is an adaptive resin or compositesystem. The term “composite” is commonly used in industry to identifycomponents produced by impregnating a fibrous material with athermoplastic or thermosetting resin to form laminates or layers.Generally, polymers and polymer composites have the advantages of weightsaving, high specific mechanical properties, and good corrosionresistance which make them indispensable materials in all areas ofmanufacturing. The use of other fabrics such as carbon nano-fibers,spandex, chopped fiber, random fiber mat, fabric of any material,continuous fiber, fiberglass, or other type of textile fabric can beused to replace carbon fiber in any of the cited examples.

The preferred DMR to use in forming the resin system or composites usedin the presently claimed device is shape memory polymer (SMP). SMPmaterials “heal” via two mechanisms. First, SMPs have memorized shapes,allowing them to return to form upon thermal activation above T_(g).Secondly, SMPs perform a reptation process, where long polymer chainswithin a thermoset matrix will move freely and entangle at temperaturesabove the T_(g) of the thermoset and thermoplastic. When the Tg of theSMPs are above the Tg not only does the elastic modulus of the SMPdecrease dramatically, but additionally, the increase in temperatureincreases the mobility of the long chain polymers within the SMP acrossa boundary.

Because of the properties inherent in shape memory polymers, compositesutilizing shape memory polymer as the resin matrix can be temporarilysoftened, reshaped, and rapidly hardened in real-time to function in avariety of structural configurations. SMPs can be fabricated with nearlyany type of fabric, and creative reinforcements can result in dramaticshape changes in functional structures and SMPs have the additionalbenefit of being highly machinable.

SMAs and SMPs that have been pre-formed, with a memory shape, can bemore easily deformed to a desired shape above their glass transitiontemperature (Tg). The SMA and SMP must remain below, or be quenched tobelow, the Tg while maintained in the desired shape to “lock” in thedeformation. Once the deformation is locked in, the SMA, because of itscrystalline network, and the SMP, because of its polymer network, cannotreturn to its pre-formed, or memory, shape due to thermal barriers. TheSMA and SMP will hold its deformed shape indefinitely until it is heatedabove its Tg, whereupon the SMA and SMP stored mechanical strain isreleased and the SMA and SMP returns to its pre-formed, or memory,state.

Many sources claim that there is an interchangeable nature between shapememory alloys (SMA) and shape memory polymers, however, for manyapplications this is not so. The technical difference between SMA andSMP at the molecular level is in the linkages between molecules. SMAessentially has fixed length linkages that exist at alternating anglesestablishing in a zigzag patterned molecular structure. Reshaping isachieved by straightening the angled connections from alternating anglesto straight forming a cubic like structure. Recovery to memory shape isachieved by heating the material above a certain temperature at whichpoint the molecules return to their original zigzag molecularconfiguration with significant force thereby reestablishing the memoryshape. Locally, no more that eight percent (8%) strain is recoverablewith the memory effect. The molecular change in SMA is considered ametallic phase change from Austensite to Martensite which is defined bythe two different molecular structures.

SMP has connections between molecules with some slack. When heated theselinks between connections are easily contorted, stretched and reorienteddue to their elastic nature as the SMP behaves like an elastic materialwhen heated, when cooled, the shape is fixed to how it was being held.In the cooled state the material behaves as a typical rigid polymer thatwas manufactured in that shape. Once heated the material again returnsto the elastic state and can be reformed or return to the memory shapewith very low force. Unlike SMA which possesses two different molecularstructures, SMP is either a soft elastomer when heated or a rigidpolymer when cool. Both SMA and SMP can be formulated to adjust theactivation temperature for various applications.

Typical SMP materials can switch in elastic modulus by at least threeorders of magnitude becoming at least three orders of magnitude softerthan SMA materials. Although SMA materials can be switched from aslightly softer state to a stiff state, they change less than an orderof magnitude remaining more stiff than SMP in the stiff state. Forexample, this is like the difference between inflating an aluminum sodacan versus a common balloon where the balloon will expand and conformdramatically at low pressure. Conversely, an aluminum can would bulgeand subsequently burst after minor shape change and higher pressure.Another example to consider would be the difference between shaping asoft sheet of rubber versus a typical sheet of metal. SMP materials havebeen shown to replicate complex shapes of large and small size.

SMP materials have been shown to replicate surfaces with less than 10nanometer root mean squared surface roughness. This favorableperformance characteristic enables class A finished surfaces to beachieved without subsequent surface preparation and painting typicallynecessary to achieve final surface qualities for composites. Not onlycan SMA not approach the level of surface quality performance of SMP,typical surface qualities necessary for the composite industry are notachievable with corrugated SMA.

The cost per pound differences are more than an order of magnitudegreater for metals versus polymers and the difference in density adds anadditional factor of six times the cost, bringing the cost advantage atthe most general comparison level to 10 to 60 times in favor of SMP.This general comparison would be the best approach in considering eachmaterial in the lowest commodity level at extreme production volumes. Atlow volumes the cost advantage of SMP over SMA becomes more significant.Lastly considering lifecycle of the two materials used to make the samedevice, SMA devices may offer more cycles than an SMP device in certaincases however this advantage would be limited to no more than 2 timesgreater at best and only in rare situations.

If SMA was used instead of SMP for the presently claimed device the costof the materials and production would be significantly higher.Additionally it would require at least 100,000 to 1,000,000 psi of airpressure to assist the SMA to return quickly to is memory shape and thecrack would have to be repaired by a human operator on the ground. Suchsources of such extremely high air pressure are not easily available andnot feasible in most commercial uses such as cars, aircraft, and homes.Additionally, if the damage to an SMA results in over eight (8) percentstrain, it will be impossible for the SMA to fully recover its original,memory, shape.

However, SMP in the soft state will require little, if any, air pressureto return the SMP or SMP composite to its memory shape. This amount ofair pressure is readily available in most manufacturing facilities andcan easily be incorporated into a commercial product. Finally, anyattempt to replace SMP with thin sheets of SMA would yield a nonfunctional product as the stiffness of the thin sheets of SMA would notprovide adequate structural and mechanical properties for mostapplications.

Integrating thermoplastics into existing SMP resins by either dissolvingcommercially available thermoplastics in the resin or by in-situpolymerizing thermoplastic monomers in the resin during cure isdifficult. Thermoplastics do not easily dissolve in the resin; hightemperatures and extended time periods were required to dissolverelatively low amounts of thermoplastic (two to five percent (2-5 (¼)wt). The in-situ polymerization process prevents time-consumingdissolving step; however, many new variables arise with this process,including thermoplastic monomer selection, molar ratio of monomers,total weight loading of monomers, use and loading of initiator, and curecycle selection. Although thermoplastic networks were successfullyestablished in the SMP matrix, the extent of reaction and repeatabilityof the polymerization posed issues requiring substantially moredevelopmental time than currently described polymers.

While the styrene based SMPs described in Tong '481 are preferred, themost preferred resin system is an epoxide monomer that resembles a longthermoplastic chain but with epoxide functional groups. All monomers arelow viscosity, easily dissolve in the epoxy resin, and qualitativelyenhances the “stickiness” and “healing” ability of the material. Themethod of incorporating mono-, di-, or multi-functional long chainepoxides in the epoxy SMP matrix qualitatively gives the best healingproperties. Many such epoxides are available commercially to enhancefurther the healing properties without sacrificing the mechanicalproperties of the material. The Epoxy SMP resins used are disclosed inPCT application number PCT/US2006/062179 and are commercially availablefrom CRG Industries in Beavercreek, Ohio, U.S.A. athttp://www.crg-industries.com.

Those of skill in the art should be able to select the proper materialfor the application based on cost, mechanical properties desired, andtype of resin desired. The material selection for the disclosed deviceinvolves the selection of a resin system, the optimization of itsmechanical properties, and the incorporation of self-healing mechanismsinto the resin. Based on the application requirements and the wide rangeof resin systems available, the resin system can be designed to exhibita T_(g) between 0° C. and 280° C. The mechanical properties will meet orexceed those of conventional resins of the same chemistry. Theelongation and recovery of the material above T_(g) can be designed tobe between 0% and 100%, allowing most minor and major deformations toreturn to original form.

The healing time is important to fully understand and optimize thehealing cycle. In optimizing the healing times the system will only heatthe damaged sections for the minimum required time. In removing excessheating time the system will require less power, therefore reducing thepower draw. In addition to limiting the power draw on the system thisapproach also minimizes the structural change. Current reptation modelsshow the time to heal at a boundary to be five hundredths of a second.The full healing time, which includes the time for the SMP or SMPcomposite to return to its memory shape, is on average 3 minutes to healfully. The time difference is believed to stem from the time needed toheat the composite, and to cheat low heat transfer coefficients ofcomposites.

Those of skill in the art should be able to find the time to heat andrepair a given system. First the thermal conductivity, specific heatcapacity and mass densities must be found in order to correctly modelthe time to heat the system. An infrared camera can be used to directlymeasure the composite. This method will utilize the Kapton® heaters toheat the bottom of the composite system while recording temperatures onthe top side with the IR camera; in addition to finding the time torepair the system the IR camera will also check how evenly the compositeis heated.

The currently claimed device can use either a thermoplastic or thermosetDMR, DMR composite, SMP or SMP composite in the process. The mostpreferred type of resin is a thermoset SMP which provides an order ofmagnitude higher stiffness than previous state-of-the-art thermoplasticSMPs. This added stiffness coupled with high strain capability enablesthe development and use of a highly useful material for use in theclaimed process. Such polymers are described in U.S. Pat. No. 6,759,481issued to Tong, on Jul. 6, 2004 which is incorporated herein byreference. Other thermoset resins are seen in PCT Application No.PCT/US2006/062179, filed by Tong, et al on Dec. 15, 2006; and PCTApplication No. PCT/US2005/015685 filed by Tong et al, on May 5, 2005 ofwhich both applications are incorporated herein by reference. All ofthese polymers are commercially available from CRG Industries, Inc. inBeavercreek, Ohio, U.S.A. at http://www.crg-industries.com.

Damage Detecting Sensors

Another element of the claimed system is the sensing system. Any methodor means of sensing damage that can be incorporated into a product'sstructure will work. Most commercially available damage sensing systemsuse embedded piezoelectric sensors and is the preferred embodiment. Onesuch system is made by Acellent Technology, Inc. based in Sunnyvale,Calif. Acellent Technology's sensor are the most preferred sensors tointegrate into a DMR or DMR composite that can correctly identify damageand alert a controlling system of the location, amount, and type ofdamage present. Those of skill in the art will be able to customize asensor system for a desired system. While placement of the damagedetecting sensors can either be internal or external to the DMR or DMRcomposite, the preferred location is internal as discussed below.

Activation Elements

Another element needed is the means to activate the DMR. As usedthroughout this application the term “activate” means to enable the DMRto switch from a high elastic modulus to a low elastic modulus. As usedthroughout this application the term “deactivate” means to enable theDMR to switch from a low elastic modulus to a high elastic modulus.

The means for activating and deactivating the dynamic elastic modulusresin (DMR) can be thermal, light, water, electromagnetic radiation, andother means which will induce the dynamic elastic modulus resin matrixto change its elastic modulus from a hard state to a soft state andreverse that state upon application of the opposite stimulus. Forthermally activated DMRs the stimulus can be the application and removalof heat. For electromagnetic radiation activated DMRs the stimulus canbe application of one wavelength and energy of light and then theapplication of a second wavelength and energy of light. The Tong patentspreviously noted can create DMRs that can heal in a few minutes or less.

There are multiple means of activating and deactivating a DMR including,but not limited to, thermal energy, light, other electromagnetic wavetypes, magnetism, water, exposure to certain chemicals and substances,and other means which are known in the art. The most preferred method ofactivating and deactivating a DMR is thermal energy through theapplication and removal of a heat source, most preferably throughresistive heating elements embedded in the product's structure.

Composite panels which integrate the activation means and the DMR or DMRcomposite composing of discrete heating elements through theincorporation of a foil etched Kapton® encapsulated resistive heatingelement is the most preferred method of applying and removing heat. Thediscrete heater should be integrated at the top ply of the DMR or DMRcomposite and processed during the DMR or DMR composite fabrication. Toprotect the thermoplastic coated diodes and solder pads, a layer ofKapton® film is added over the top of the heating element prior toprocessing. Encompassing the diodes into the package allows the discreteheater to be placed mid-ply in the composite and minimize heat energylost to the ambient, a concern that will only amplify when dealing withforced convection during flight or other motion.

The added layer of Kapton® film is sealed to the resistive heater usingtape around the perimeter. The excess tape is trimmed off leaving thebottom surface unaltered. The enclosed heating element is then placedatop the composite ply schedule of pre-preg carbon fiber and healableDMR matrix, and more preferred SMP matrix, is pressed down using asqueegee. The composite is then vacuum bagged and cured. Once thecomposite is cured the vacuum bag is removed and the tape can be removedfrom the localized heater exposing the solder points and diodes. As aresult of the heater and composite being co-cured there is good adhesionbetween the Kapton® film and the composite panel.

The design of the preferred heater pad, 4, is shown in FIG. 1. Theheater sections, 2, are evenly spread throughout the pad with theelectrical bus bars, 6 and 8, providing the necessary paths for the flowof electricity to the individual heater sections, 2.

The layers of the heater sections are shown in FIGS. 2-5. The firstlayer, shown in FIG. 2, is a Kapton® layer, 10, with holes, 14 and 12,in it for electrical connections to the other layers. The leads of adiode, to prevent the two-way flow of electricity through the heaters,is passed through the holes, 14 and 12, on the first layer, 10, andholes, 30 and 38, of the third layer, 32, as shown in FIG. 4, andfinally connected to the leads of the heater, 18 and 16, on the fourthlayer, 22, shown in FIG. 5. FIG. 3 shows the bus bars, 38, used to allowcurrent flow. These bus bars are sandwiched between the first and thirdlayers so that the bus bar, 38, in FIG. 3 aligns with the hole, 26, inthe third layer, 32, and the connector, 20, in the fourth layer, 22.FIG. 4 is an electrically insulating Kapton® layer, 32, to prevent thebus bars, 38, in FIG. 2, from contacting other bus bars, in FIG. 5. Theholes, 30 and 38, are lined up with holes, 14 and 12, on the first layerso as to allow electrical connections between the Kapton® layers.

The preferred design of the heating panel is an array of 64, 1 inchsquare resistive heating elements spaced at approximately 1.5 inch oncenter. The package is a 5 layer polyimide package to insulate theheating elements from the composite, insulate the bus bars from eachother, and to protect the top surface from environmental degradation.Each resistive heating element is designed for 8 ohms resistance, whichwill provide a power density of 2 watts/in̂2 when supplied with 0.5 A at4 volts. Using the above power, localized heating of at least 115° C.can be achieved, while maintaining the temperature of surroundingelements at approximately the current environmental temperature.

The preferred design uses bus bars capable of higher current drawwithout heating, resulting in thinner traces. This allows a user toplace the heaters closer together, allowing a more finely tunedactivation area when repairing damage. With the integration of the wiresinto the Kapton® package, the wires are run to a central locationsimilar to the sensing layer. The Kapton® package will have receptorsfor solder points to attach surface mounted molex connectors that willinterface directly with the intelligent control system.

Localized heating is achieved by selectively activating the heatingelements. Temperatures ranging between 115° C. and 130° C. can easily beachieved and higher temperatures are possible with proper design. Byincreasing the power to the resistive heating element, temperaturesabove 130° C. can be achieved; additionally the use of variously heatingelements and resin can also affect the temperatures. Those of skill inthe art will be able to determine what temperatures must be obtained bythe heating element to heat the entire composite panel to activationtemperature. Additionally those of skill in the art will be able todetermine the optimum placement in the composite for both uniformthermal distribution and composite mechanical properties.

Those of skill in the art can also design a system that reduces theparasitic weight of the discrete activation layer in the DMR or DMRcomposite system. The referred way to reduce this parasitic weight is todesign heating elements with leads integrated into a Kapton package.These leads were designed as copper traces that were chemically etchedaway on a Kapton substrate. Those of skill in the art will be able todesign a heating system which satisfies the needs of the system withoutcausing damage through improper heater spacing and thermal gradients.

Incorporating the current design of the discrete heater into the mid-plyof the composite would result in shorting of the circuit due to theconductivity of the carbon fiber and the diodes being surface mounted onexposed solder pads. Also, due to the thickness of the diodes, reducedmechanical performance is also a possibility as a result of continuousfibers deflecting out-of-plane. While thin film transistor (TFT)networks to distribute electric current to discrete points toresistively heat the composite could be used, the technology is stillnew and bulky that lower profile diodes and diode alternatives arepreferred.

Integration of Activation Element, Sensing Element, and DMR Element

The preferred panels of the reflexive structure were fabricated using 3k plain weave carbon fiber and styrene based healable SMP resin systemas described in U.S. Pat. No. 6,759,481 issued to Tong by integratingAcellent's SMART Layer® sensing system at the mid-ply and the Kapton®discrete heating element at the bottom or back ply of the panels,leaving the side of the panel which will be exposed to the surroundingenvironment to be the resin or composite. Incorporating the non-porousresistive heating element into the composite ply schedule required thedevelopment of a process to pre-preg styrene based SMP matrixcomposites. The developed process used a vacuum assisted resin transfermolding (VARTM) process to infuse carbon fiber fabric with styrene SMPin a closed mold. The parts were cured for 1 hour and 45 minutes in anoven at 75° C. to gel cure the resin. The gel cured parts were then cutto shape and used in the composite ply schedule as standard pre-pregmaterial. The parts were then vacuum bagged and fully cured in a closedmold. Precautions were taken to protect exposed electrical connectionsin both the heater and sensor layer by coating exposed connections withchemically resistant tape.

Once the parts were fully cured they were demolded from the vacuum bagand glass and the tape was removed exposing the electrical leads.22-guage wire leads were soldered to the discrete heater on all 32solder pads. Flat ribbon cable was soldered to the Acellent SMART Layer®with a male connector at one end interfacing with the Acellent hardware.

The ability of the sensing layer and Acellent health monitoring systemto identify location and magnitude of structural change requires adetermination of the optimal wave form to identify structural damage.The system offers a variety of potential wave forms for characterizationincluding waves with 3, 5, and 10 peaks as well as bursts and chirps.The system also offers the capability for user defined wave forms.Resolution analysis on repeatable structural changes should be run todetermine which combination of wave forms has the highest resolution ofstructural change.

Active scanning systems from Acellent can be used to drive a 3×3 sensorgrid array that is integrated into the reflexive system panels. ThisAcellent active imaging system collects data from the sensor grid, andproduces a ¼ inch spatial resolution data file that represents themechanical fatigue of the respective 11-inch square inspection area.

The sensing layer is integrated at the mid-ply of the composite plyschedule to optimize sensor resolution. The sensor is integrated intothe composite during the fabrication process to minimize the potentialfor void introduction and optimize bonding. The integration processconsists of assembling the bottom plies of the composite using thecarbon/Stryene SMP pre-preg then placing the sensor at the mid ply andassembling the remaining layers of the composite ply schedule on top ofthe sensor. Pressure is then applied between each layer with a handsqueegee to ensure good adhesion between plies. The composite panel wasthen vacuum bagged and cured completely.

The appropriate set of signal parameters allowing for the generation ofaccurate data will only be accurate for the preferred embodiment of aspecific composite ply schedule of the composite panels fabricated withthe sensing layer at the mid-ply; however, a process capable of reducingthe amount of time needed to identify optimal parameters is disclosed.By creating a baseline data set and comparing that baseline to a futuredata set, a control system can automatically determine where the damagehas occurred, how big the damage is, and the proper sequence to repairthe damage.

This process requires an initial effort to run scans at a variety offrequencies, gains, and signal types at each of the respective anglesthe signal could travel. In the current sensor layer, the piezoelectricsensors are equally spaced in the X and Y directions limiting the anglesthe waves have to travel to ±ninety degrees)(±90° and ±forty-fivedegrees)(±90°. The scans are run on un-damaged panels to allow for theuser to analyze the data and identify trends as to which set ofparameters yields the highest sensitivity. The sensitivity of the systemcan be identified through an analysis of the sensed signal strength inan undamaged panel. Sets of parameters yielding higher sensitivity willhave higher received signal strength in undamaged panels, while sets ofparameters with lower sensitivity will have lower received signalstrength in undamaged panels. The selection of sensitivity is directlyrelated to the type of and extent of damage being identified by thesystem.

The preferred panels are capable of identifying and healing damage of aleast ninety-five percent (95%) of original form and can be designed toheal one-hundred percent (100%) of original form. The preferred panelsfabricated are 12″×12″ squares with integrated piezoelectric sensinglayers at the mid-ply and Kapton® encapsulated foil etched heatingelements capable of discrete heating co-cured at the top ply. Thepreferred DMR is a styrene healable SMP resin system due to the maturityof the system as well as its ability to consistently heal over ninetypercent (90%) of damage.

Using this process those of skill in the art will be able to generatethe proper set of scanning parameters for subsequent panels quickly.This is important for the commercial fabrication of the panels. Theobvious design goal of this process is to develop a set of panels withoptimized performance of heater design and minimize the parasitic weightof the panels through the reduction of weight associated withnon-structural components in other healing systems.

The preferred design has minimized the thermal gradient and thermaluniformity through the reduction of bus bar width. The bus bars are ⅛inch copper bus bars connected to the 1 inch center heaters. The mostpreferred design incorporates foil etched leads that homerun to acentral location and are connected with surface mount connecters. Thismodification reduces the weight penalty of system integration throughthe elimination of 22-guage wire conductors. To further add robustnessto the design of the integrated heater a conformal surface coating isapplied to the diodes to both protect the diode as well as provide alayer of electrical insulation.

Based on the current reflexive system design the heater is integrated atthe top ply of the structure for multiple reasons including ease ofdiode repair as well as a result of the lack of electrical insulation incarbon fiber. One large trade-off of integrating the heater at the topply is the heat losses to the surrounding ambient environment associatedwith the placement. A much more efficient design is to integrate theheater at the mid-ply of the composite to maximize the generated heatinto the composite structure.

To integrate the heater to the control system, Molex pin connecter and22 gage wire bundles are used. Following the damage prioritization andselected healing cycle the control system applies a voltage drop acrossthe selected leads to generate heat. This approach is the moststreamlined approach, however due to the design of the control systemthis approach only allows for the application of 5V to each heater. Toincrease the range of performance of the system, an interface runningbetween the control system and the discrete heater can be fabricated.The interface is comprised of mechanical relays and a DC power supplythat will allow both a higher and lower voltage drop to introduce moreor less heat based on both the resin formulation and ambient conditions.This interface will also allow a control system or human operator todetermine what power densities are required to heal composites ofdifferent thicknesses and ply schedules.

An electrical schematic of the selective nature of the heaters is shownin FIG. 6. The array of horizontal lines, D, E, and F and verticallines, A, B, and C in FIG. 6 represent bus bars with the ability tosupply power to locally heat the small resistive heating elements oncethe bus bars are connected to a power source. The bus bars can beconnected to a power source manually or through switches that turn thepower on or off. The heating elements are represented by the commonlyaccepted resister symbol. Additionally, diodes are placed in-line withthe resistive heating elements and only allow the current to flow in onedirection through the circuit. The vertical and horizontal bus bars areelectrically insulated from each other where they meet. This electricalisolation between the horizontal and vertical bus bars allows current toonly flow one way through the system of parallel circuits resulting inlocalized activation without bleed-off to surrounding heaters. Forexample, as shown in FIG. 6, if power is connected to Bus Bars D and B,then current can only flow through one heating element, 40, because ofthe in-line diode, 42. Additionally, it will be apparent to those ofskill in the art that the amount of heat generated is controlled by theamount of power applied to the elements.

The preferred embodiment consists of multiple components, including anintegrated piezoelectric sensor, a computer and algorithm capable ofanalyzing the change in wave propagation to identify damage, a polymermatrix composite with modified SMP resin capable of healing with theapplication of heat, and a DC power supply interface and mechanicalrelay instrument that allows to vary the voltage drop across theresistive heating elements. This system has demonstrated the ability tosuccessfully identify damage, heal the damage and verify a restorationof mechanical properties.

The delivered control system has the ability to import data generatedfrom the Acellent structural health monitoring (SHM) system, analyze andprioritize the damage based on user defined criteria, determine theappropriate healing cycle, and apply a voltage drop across theappropriate heaters all while keeping the user informed of its status ona LCD monitor. The control system is comprised of a custom printedcircuit board, DC power supply and associated capacitors, programmablemicroprocessor, custom enclosure, and cooling fan.

As part of the functionality of the Acellent (SHM) system, a variety oftailorable functions exist that dictate how well the system monitors thehealth of the structure. These functionalities are built into the systemto allow for its application to multiple structures comprised of varyingshapes, sizes, and materials. The functionality of the system allows theuser to define such criteria as wave form, frequency, gain, samplingpoints, and other functionalities.

The first step in integration of the sensor system with the compositestructure is to tune in the SHM functionality to identify varying typesof damage. If the system is not tuned into the structure properly, theSHM system will not identify the damage with the proper magnitude andlocation. Due to the unlimited number of potential combinations ofvariables, a matrix design approach varying only one criterion at a timewhile keeping the others constant is preferred. After each run it shouldbe noted how well each combination of variables identifies the damagelocation and what the magnitude of damage was. The results of thiseffort will yield a more complete understanding of the SHM system andhow each variable affects the accuracy of the scans. One critical pieceof information that is gained during this effort is the recognition thatwhen dealing with integrated SHM of an an-isotropic composite structurethe wave forms propagate differently when going in the direction of thefibers, such as at zero (0) or ninety (90) degrees, or when going at anangle to the fibers of forty-five degrees) (±45°. The completion of thisinvestigation results in the identification of a combination ofvariables that allow the SHM to use the same parameters betweenreflexive composite structures fabricated using the same ply scheduleand processing methods. Thus for every type of ply schedule andprocessing method, these tests should only be needed to be run once.

A critical component to the successful integration of each subcomponentinto a functional reflexive system is the ability for the control systemto read, interpret and interoperate the output data from the SHM system.To accomplish this task, an added functionality of the SHM system tooutput an ASCII file of the raw data comprised of location and magnitudeinformation was devised by Acellent Technologies. The ASCII files arenamed by date and a post-script number that identifies which is the mostrecent data file when more than one data file is created per day. Theintelligent structural control system then imports the raw data andlooks at the data based on user defined criteria that includes damagemagnitude, damage location, physical size of damage, and otherparameters that were deemed relevant. Based on these criteria, thecontrol system assigns a damage value to each damage location forprioritization. The location with the highest damage prioritization ishealed first.

Control and Operation

In order to optimize the control system, it is necessary to determine anappropriate algorithm to prioritize the damage locations, if multipleimpacts were to occur, as well as develop a method to address damagedareas in the event that the damaged area required more power to healthan is provided by the system. By evaluating what would be mostimportant to increasing the survival of a product and then using apriority ranking system to weigh each aspect an algorithm and system canbe easily developed by those of skill in the art. Aspects to consider increating the algorithm and system include, size, magnitude, location,and magnitude of surrounding rankings. Using the algorithm, each damagearea is assigned a numerical value for direct comparison with otherdamage sites. The control system then finds the highest number andbegins by healing that area first. Those of skill in the art should beable to design an algorithm to prioritize the damage locations, ifmultiple impacts were to occur, as well as develop a method to addressdamaged areas in the event that the damaged area required more power toheal than is provided by the system

The process is shown in FIGS. 7-11. In FIG. 7, a damaged area, 50, isshown. The causes of the damage, or the products on which the damageoccur, are irrelevant, however, for the purposes of this description thedamage has occurred on the wing of an aircraft. In FIG. 8, the sensors,54, of the sensing system, have detected damage in an area, 52, of thewing. The system will next determine if the damage can be healed in onestep or requires multiple, sweep, healing. Upon identification of thedamage location with the highest prioritization, the control system willthen look at how many heaters are required to heal the damage at thatlocation. This step is completed by examining the physical size of thedamage and the magnitude of the surrounding areas of the damage. Tomimic an aircraft environment and to minimize the stiffness change inthe composite structure, limited the number of heaters that can beactivated at any given time to six (6), which corresponds to a six (6)inch square physical area. If a damage area requires more than six (6)heaters to be activated to heal the damage the system beings a sweephealing process that activates six (6) heaters for healing thenactivates six (6) adjacent heaters and so forth until the entire damagearea is healed. The system also has a top end limit of heaters that thesystem will activate at any given time before it recommends a systemabort. If the damage magnitude is too large or extreme for the reflexivesystem to repair, the system will recommend an ejection or replacementof the part.

After the scan of the damage area is complete, a file is generated,downloaded and processed in order to determine the location(s) requiringhealing. The algorithm used for this processing includes two modes. Modeone operation includes default values for all parameters and thresholds.Mode two operation prompts the user to select the parameters used forprocessing. The results of this algorithm are passed to the “healingalgorithm” which selectively activates a 10 heater×10 heater power gridof 12″×12″ in physical size in order to heat and thus heal target areasas shown in FIG. 9. In. FIG. 9 the heaters, 56, are selectivelyactivated by the control system so that the damaged area, 58, is raisedabove its Tg and healed.

While automatic control systems to determine the amount of damage andthe proper sequence of healing and activation are preferred, the systemcan be designed so that a human user can determine and activate theproper sequence. Alternatively the system can be designed for control byan automatic system or user input depending on the damage and availabletime to repair the product.

Once the “Active Healing” cycle is complete, the user is prompted toinitiate another inspection of the product using the Acellent system asshown in FIG. 10 after the temperature of the panel has been loweredbelow the Tg. In FIG. 10, the sensors, 60, determine that the area, 62,has been healed. Then the above procedure is repeated until the healingalgorithm determines that no additional healing is needed as seen inFIG. 11. During this entire process, the user is constantly updated withthe status of the healing via a graphical LCD display panel. A portableyet powerful Rabbit Semiconductor microcontroller is the preferred heartof the control system, and it has been used to demonstrate thecapability of monitoring the files and downloading the files as neededfor processing. The isolated power drive circuits have been designed andtested as well. These include GMR (giant magnet-resistive) sensors toserve as a low cost, and miniature means for current measurement of allpower lines feeding the healing grid. The traditional means for currentmeasurement include bulky and expensive coil packages. This GMR currentinformation will be useful in identifying open power lines due to severeimpact damage. In the event of an open power line, power will bererouted to the surrounding closed lines for healing. This feature wouldbe used in the event of puncture damage or severe impact damage.

INDUSTRIAL APPLICABILITY

The claimed method and devices can be used to create a self-healingsystem for aircraft, automobiles, buildings, other structures, and anyproduct that uses resins or composites.

1. A method of healing a material comprising: a sensing means fordetecting damage at a damaged point in a material; a repair means forrepairing said material at said damaged point; and a control means forselectively activating the repair means at the damaged point.
 2. Themethod of healing a material of claim 1 wherein said means for detectingdamage is a continuous health and performance monitoring system.
 3. Themethod of healing a material of claim 2 wherein said continuous healthand performance monitoring system is an embedded piezoelectric sensorsystem.
 4. The method of healing a material of claim 1 wherein saidmaterial is an adaptive composite structure.
 5. The method of healing amaterial of claim 4 wherein said adaptive composite structure is afibrous material in a dynamic elastic modulus resin matrix.
 6. Themethod of healing a material of claim 5 wherein said dynamic elasticmodulus resin matrix is a shape memory polymer matrix.
 7. The method ofhealing a material of claim 1 wherein said material is an adaptive resinstructure.
 8. The method of healing a material of claim 7 wherein saidadaptive resin structure is a dynamic elastic modulus resin matrix. 9.The method of healing a material of claim 8 wherein said dynamic elasticmodulus resin matrix is a shape memory polymer matrix.
 10. The method ofhealing a material of claim 1 wherein said repair means activates anddeactivates a self-healing mechanism in said material.
 11. The method ofhealing a material of claim 10 wherein said self-healing mechanism isactivated and deactivated with thermal energy.
 12. The method of healinga material of claim 10 wherein said self-healing mechanism is activatedand deactivated with electromagnetic waves.
 13. The method of healing amaterial of claim 12 wherein said self-healing mechanism is activatedand deactivated with visible light.
 14. The method of healing acomposite material of claim 10 wherein said self-healing mechanism is acombination of a first self-healing mechanism and a second self-healingmechanism.
 15. The method of healing a material of claim 14 wherein saidfirst self-healing mechanism is a shape memory effect.
 16. The method ofhealing a material of claim 14 wherein said second self-healingmechanism is reptation of said material across said damaged point. 17.The method of healing a material of claim 1 wherein said control meansfor selectively activating the repair means at the damaged point is acomputer control system interfaced with said sensing mean, said repairmeans and said material.
 18. The method of healing a material of claim17 wherein said computer control system: a. compares a baseline data setagainst a first new data set; b. determines a healing process based onthe comparison between the baseline data set and first new data set; c.creates a set of tasks capable of being carried out in the propersequence by a machine to execute said healing process; and d. comparessaid baseline data set against a second new data set to determine whensaid healing process is complete.
 19. The method of healing a materialof claim 1 wherein said means for selectively activating the repairmeans at the damaged point is by manual input from a user.